It is known that fuel injectors, used to inject a fuel-air mixture in the combustion chamber of an engine can be injectors, principally piezoelectric or solenoidal. In particular, injectors are driven by electronic controlling devices that comprise a power stage designed to drive them with a proper current or voltage signal.
It is also known that the standard control techniques for current generation in the power stage of the aforementioned devices are principally PWM or average current mode stages. Even if they do not present sub-harmonic instability, they actually introduce delays with respect to the switching frequency; thus, those delays force the designers to construct control loop stages operating with a frequency that is at least three or four times lower than the switching frequency of the power stage.
To solve this problem, control loop stages have been designed with a reduced time delay; that type control loop stages operate typically with two different circuit configurations, known in the art as a “peak current mode circuit” and “valley current mode circuit”. Driving fuel injectors with “peak current mode circuits” or “valley current mode circuits”, even if produces a reduced time delay, present instability.
In fact the power stage typically operates over MOS or FET transistors having a common switching node connected to the load (the injector) that presents a lot of ringing due to the reactive parasitic components. Since the control loop stages operate sensing the current on that node, there is the need of a blanking time before the sensing (typically around 300 ns). In particular when the load presents a very high duty cycle (bigger than 50%), sub harmonic instability occurs.
The peak or valley current mode circuits instability can be solved by using circuits with hysteretic current mode circuits, with a quasi-constant period that provide adequate stability of the current control loop. Nevertheless, the known circuits still present some disadvantages; on one hand they do need particularly complex circuits that make the measurement of the frequency (or the period) very convoluted. On the other and, they do not give sufficient performances when used with injectors that operate with high frequencies. In particular, if the injector operates with frequencies higher than a hundredth of kilohertz, the switching frequency becomes too high for those circuits, thus making a stable and simple control loop stage technically not feasible.
In view of the foregoing, it is at least desirable to provide a hysteresis-type electronic controlling device for fuel injectors that is free of the aforementioned disadvantages. It is also at least desirable to provide a fuel injector control method. In addition, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.